MOS Technology Advert - September 1975

The image above is adapted from a Wikimedia public-domain source^[1]

MOS Technology was founded in Valley Forge, Pennsylvania, in 1969 by three former employees of General Instruments. It was set up in order to be a second-source provider of Texas Instruments' chips for electronic calculators, with the name MOS meaning Metal Oxide Semiconductor - a type of transistor fabrication process.

A couple of years later, Commodore - a company established in Canada in the late 1950s as a typewriter business - launched its first calculator, a re-badged Bowmar model.

Commodore quickly established itself in the calculator market in competition with companies like Hewlett-Packard and Texas Instruments, but then the latter started selling its own calculators for less than the cost it sold the parts for to other companies.

The ensuing "Calculator Wars" led to the collapse of several chip suppliers and calculator companies, including Bowmar - which insisted on keeping its machines selling for up to $500 whilst TI's were selling for $49^[2] - but Commodore managed to survive.

MOS was also affected, but hung on partly by selling chips to Atari for its Pong video game.

Meanwhile, a team of designers who had been working on Motorola's 6800 - a CPU used in several early microcomputer systems such as Midwest Scientific Instruments' MSI 6800 and various SWTPC micros - left the company in 1975 because they had been prevented from working on a much cheaper follow up^[3].

The team - which included 6800 co-designers Chuck Peddle and Bill Mensch - ended up finding a home at MOS Technology, where they quickly got to work on their new processor.

Two CPUs were developed as part of this 6500 line - the MCS6501, which was pin-compatible with the original Motorola 6800, and the MCS6502 which was not, although it was the same as the 6501 internally.

Motorola almost immediately sued MOS over what it saw as an infringement, and as part of the eventual settlement the 6501 was canned.

However, the 6502 was allowed to continue, although as no customers were yet using it, MOS ended up having to create the KIM-1 single-board micro, with a small hexadecimal keyboard for input and a calculator display for output.

The KIM-1 became one of the most popular small/kit microcomputers, but by 1976, MOS's calculator supply market had collapsed, leading to financial problems - even though by now the 6502 was also starting to sell well, largely because at $25 it was the cheapest CPU on the market by far.

Back at Commodore, the experience gained during the Calculator Wars was not lost on Commodore's CEO Jack Tramiel, who noted that it was TI's vertical integration which had allowed it to sell its calculators for much less than anyone else.

And so towards the end of 1976, Commodore ended up buying MOS Technology, on the understanding that Chuck Peddle and his team would be part of the deal. That gave Commodore the 6502 and the KIM-1, as well as a guaranteed supply of all the semiconductor chips it needed.

Accounts differ on what triggered Commodore to create the PET, with one suggestion that it was Peddle who said to Tramiel that calculators were a dead end and that the company should move into microcomputers.

However, according to his book The Home Computer Wars, Commodore insider Michael Tomczyk wrote that when Peddle and Tramiel were discussing the 6502 after the acquisition of MOS, Tramiel was reported to have said:

"You know what you've got here? You've got the makings of the first low-cost personal computer!"

Either way, Peddle was given six months to produce a computer - with Commodore announcing it to the press towards the end of 1976.

He assembled a team which included Bill Seiler, John Feagans, one of Jack's sons, Leonard, and some engineers from Japan.

Prototype machines were shown in early 1977, with the actual computers - by now known as the PET, for Personal Electronic Transactor, or sometimes less favourably as Peddle's Ego Trip - being formally unveiled at CES in June 1977^[4].

The 6502 and its derivatives ended up being used in many microcomputers and video games of the day, including the VIC-20, Commodore 64, BBC Micro, Oric Atmos, Apple II and Atari's 2600/VCS. MOS also designed and built many of the support chips used in Commodore's computers, right up to the Amiga.

The ARM 1 - a spiritual ancestor of the 6502. From Practical Computing, October 1986

It was also the chip - thanks to its use at UK company Acorn - that inspired the architecture of the Acorn RISC Machine, or ARM processor, now used in countless millions of smartphones.

This was in part because many of the 6502's instructions ran in a single clock cycle - one of the defining features of RISC chips - often making it faster than contemporary processors with sometimes four times the nominal clock speed, such as the Z80.

Sophie (then Roger) Wilson - one of the designers of Acorn's BBC Micro, and described by her peers as "probably the world's best 6502 programmer" - was said to have designed the ARM accordingly to "suit himself"^[5]